Third Wave (Hang Gliding Magazine, March 2004) By Mike Sandlin First the hang gliders, then the paragliders, and now... are the ultralight sailplanes coming to your local flying site? On a good soaring day, I load my glider on top of my truck and head for my local mountain hang gliding site, where I set up with the gang, launch, soar, land in the L.Z., and swap stories about the days flying. This has been going on for years, but this season theres a new twist: Im not flying a hang glider or a paraglider anymore, Im flying an airchair, a new species of ultralight sailplane. Im taking off from the same old launch slope that I ran down when I was hang gliding, but now I roll down the slope until I reach flying speed, and then Im off into the blue. Since this kind of launch isnt being done regularly anywhere else in the world that I know of, some explanation is called for. Over the last four or five years Ive designed, built, and flown a series of gliders that fit my idea of an airchair, essentially a garden chair with a wing. This is an ultralight sailplane that allows the pilot to fly out in the open, at low speeds, in a light, simple airframe that has been designed for basic soaring and car top transport. My latest design, the Goat, can serve as a good example. It weighs about 140 lbs. empty (complete with hand deployed emergency parachute).This is well under the ultralight sailplane weight limit of 155 lbs., so its airworthiness and pilot qualifications are not subject to direct official oversight in the United States. I fly seated, strapped in place with a four point seat belt, mostly out in the open air, like a paraglider pilot, and usually in an insulated flight suit. This exposed flying is comfortable because the Goat flies at hang glider speeds, a result of having about the same wing loading as a hang glider (i.e., the ratio of its total flying weight in proportion to its wing area is about the same as that of a hang glider). While disassembled and folded, the glider can be transported on top of my truck on my padded hang glider rack, with no special adaptations, braces, or other baggage. Under perfect conditions I can assemble the Goat, single handed, in just under twenty minutes. The rolling launch idea originated while a few friends and I were fumbling around on a training hill with one of my early prototypes, trying to do some first flights. Hang gliders on wheels had been pushed down launch slopes forever, so we tried pushing the glider down the hill and managed to get some flights, but it was awkward and perilous to the pushers. Next we tried the paraglider training technique of pulling with a short rope, but that really didnt work at all, the pull wasnt fast enough and the pullers were in the way. At last somebody suggested just letting it roll down the hill until it flew, and to the amazement of all this seemed to work about as well as anything. Eventually this became our standard launch technique both for training and for mountain launching, since it was easy to do and practical as long as the wind was adequate and the slope was smooth and open. The requirements for mountain roll launching are (1) slow flying speeds (presumably requiring a low wing loading) and (2) car top transport (the trailers wont make it up the back roads). This season my weekend soaring takeoffs have all been done by roll launching, mostly at Horse Canyon, a mountain hang gliding site near San Diego, California. At Horse the launch pad is two Goat wingspans long and drops about seventeen feet, adequate for launches in moderate winds, with reasonable tip clearance from the rocks and bushes along the sidelines. At launch, I sit at the top of the slope, belted into the Goat seat with my feet and nose skid down on the ground (the skid is held down by keeping the control stick full forward, a precaution against wind gusts). In this position I can wait for the best wind and traffic conditions before takeoff, a launch potato once again, but with a few differences from my hang gliding days. I have to persuade the launch helpers to let go and stand aside, since unlike a hang glider I usually have good roll authority while just sitting there in the wind. Good control and stability in turbulence also tempt me to go at the height of the wind cycle, rather than waiting for the smoother but lower velocity wind that follows it, to get the highest possible margin of takeoff airspeed. The launch starts when I call out clear and push against the ground with my feet to raise the nose off the ground (or, if the wind is strong enough, I just raise the nose with the elevator). Some fast foot action gets my feet onto the rudder pedals as the glider begins to roll and slowly picks up speed. I hold the wings at a level bank (controlled by sideways action of the stick) and the nose down but clear of the ground (controlled by fore and aft motion of the stick) as I steer straight down the hill with the rudder (foot pedals). The sixteen inch diameter pneumatic tire gives me a smooth ride down to the end of the slope, where I lift off the ground and dive over the bush tops until Im sure of some reserve airspeed. When Im well clear of the ridge I settle into a comfortable flying speed (30 mph. is fast in the Goat) and switch to the coordinated flight control technique where the stick and rudder are used together for turns. This business of having to coordinate foot and hand control inputs, the three axis control system, is one of the big differences between sailplane or airplane flying as opposed to hang gliding or paragliding, and its a major obstacle to a quick transition from foot launching to airchair flying. When student pilots first try to turn with a three axis system, they will usually try to use just the control stick, with the result that the wing will roll but the nose will not swing into the turn, it will just wallow in place or even go the other way. You have to use the foot pedal (rudder) to yaw the nose into the turn as well as using some side stick (ailerons) to bank the wing if you want any kind of decent turn response at all. Of course, while using these two controls in exquisite coordination, you also have to command airspeed by control stick fore and aft position (using the elevator to control nose attitude), so three axis flying can be a tricky business until you get the hang of it. The reward for using mechanical controls is fast response and not having to use as much muscle in the turns. Out on the ridge and back above launch, I can mix readily with the hang glider traffic because Im flying at the same speeds and using the same soaring techniques (typically at Horse Canyon most paragliders dont come out until later in the day when many of the hang gliders have landed). I havent measured the performance of the Goat, but I think Im flying about like the average king posted hang glider, and maybe a little slower and tighter, at times, in thermals. In a small thermal youd like to fly as slow as possible in order to stay close in to the lift core, but you cant just fly at minimum airspeed because you still have to track and follow the lift, and that requires maintaining maneuvering speed about half the time. Since the Goat has both a light wing loading and good low speed roll control, I can work small thermals comfortably and with good results. Flying seated in a busy thermal, with whirling traffic above and below, I feel a little like Harry Potter in the middle of a frantic quidditch match, although, of course, our soaring traffic is usually less chaotic (we dont see many people turning in the contra-gaggle direction). After a couple of lift cycles, having taken in the view from whatever altitude is available, I might be satisfied with my soaring and ready to fly away on a gradually descending tour of the local flying area, cruising down for a landing. Airchair landings are a lot like hang glider landings. The pre-landing checklist is the same (check the local area for other air traffic, especially on the horizon; check the wind direction; check to be sure the landing zone is clear). I fly the same box landing pattern as always, at the same airspeeds, and put out my drogue chute at about the same place (Im a big drogue parachute fan, I used them for every landing when I was hang gliding). In the pattern, the ground path is adjusted in response to turbulence and lift using the standard hang glider/paraglider practice, cutting in when low, swinging wide and staying back when being forced up. This is contrary to the general sailplane method, where you pretty much fly a fixed pattern and operate the dive brakes for glide path control, and thats what a lot of the ultralight sailplane pilots still would like to do, but I dont think its going to work for airchairs. The magnitude of lift effects at these wing loadings can be so great that maneuvering and timing are the best practical method for controlling a descent in the landing pattern . A dive break powerful enough to allow an airchair to fly a fixed pattern under extreme conditions would itself be a nemesis. Landings are generally pretty easy, you just fly a casual pattern down to grass skimming altitude and then sit there until the wheel settles onto the ground. Hang glider flares and paraglider type braking maneuvers arent needed here, since youre landing on a wheel, not on your feet, and you can just roll to a stop. If needed, the nose skid can be set down for a brake, but it may grab on soft ground, like a thin bicycle tire in sand, and it can sometimes produce a more abrupt halt than intended. A quick stop can rock the glider forward, putting the tail high in the sky, an undignified way to end a flight. The more stylish landing method is to slowly roll to a stop while lowering the tail skid and both feet to the ground (since the wheel is located is at the center of lift, the glider is only slightly nose heavy and it can be landed or launched as either a nose dragger or a tail dragger, pilots choice). For ground tow or ultralight aerotow launches (which are what most pilots elsewhere would be doing), airchairs easily fit into a hang glider operation. The tow speeds are the same, you dont need a launch dolly, the hookup is fast and simple, and there is little or no risk of a lockout or tumble. On tow, one hand is always free, ready to release, and behind an ultralight towplane the glider is stable enough that when the controls are released the only result is a gradual climb above the level tow position. On the whole, airchair towing is so casual you have to make yourself wake up and remember that this part of the flight deserves your full attention because things can go wrong. Eventually there will be airchair accidents, probably similar to foot launch accidents, more often a launch or landing bongle than a plummet from the sky. In this low speed crash situation an airchair should provide superior protection for the pilot by surrounding him or her with frangible structure, which can absorb impact energy and help isolate the pilot from ground objects. If, on the other hand, control of the glider has been lost at altitude, and something like a plummet really has developed, its time to go for the hand deployed emergency parachute, which is mounted on the side of the nose section down on the pilots right. This is an ordinary hang glider emergency chute and bridle in a deployment bag, rigged to be tossed out to bring down the pilot and glider together in the usual way. The usual way, that is, except that the bridle is set up to bring down the glider down tail first, with the nose up in the air. The plan is that at the end of a drifting parachute ride, the wing or tail will contact the terrain first and crumple up, protecting the pilot from... discomfort. My fellow local airchair pilot, Floyd Fronius, another old time hang glider pilot, has reworked the Bug2 airchair biplane and is flying it on the coastal ridge at Torrey Pines (as well as inland). His specialty is the airchair cliff launch, which can be made from level ground near the cliff edge in high winds, unassisted. Floyd also resolved our curiosity about what happens when an airchair lands in shoulder high bushes (the result: nothing dire, just a gentle forward pitch and nose bonk), and has defined the cliff launch concept of too much wind, which is when the wheel starts to rise off the ground even though the nose skid is pressed firmly into the dirt. My own educational misadventures involve landing in ruts, destroying wheels, overinflating the tire (dont do it, it locks up the wheel), and various bent tubes. The Goat airframe is constructed of aluminum tubing, bolted together and braced with steel cable, similar to conventional hang glider construction. For ease of home building, I tried to keep everything down at a garage technology level, using readily available materials and hand held tools. There are no welded or specially machined parts on the Goat. The covering fabric is light aircraft polyester (Dacron), cemented in place and shrunk to fit with a clothes iron, nominally the Polyfiber process except that I stop short and dont use the ultraviolet protection (aluminum paint) or the cosmetic paint layers. All the sensational details and the complete technical drawings are in the public domain, free for downloading from my website, home.att.net/~m--sandlin/bug.htm (or just search for basic ultralight glider). Airchairs like the Goat (in particular, the commercial Super Floater) are already flying at ultralight tow operations such as the Florida airparks, and sometime in the future we may also see them flying at mountain sites and training hills. Eventually, airchairs and faster ultralights might be a third wave at local sites, joining the hang gliders and paragliders, becoming a part of the local soaring scene. To become popular and be widely accepted, airchairs will need time to develop all the usual stuff: commercial production and certification, standardized instruction and ratings, and an organization that provides unified representation, public relations, insurance, and calendars. It isnt time yet to say look out, USHGA, here we come!, but, ultimately, using the same launch and landing areas would mean joining the same organizations. You might ask why anybody would want to fly some new type of wing if its heavier, more complex, and has no better performance that an average hang glider. Id answer that the main reason is just for the fun of it, for novelty and adventure, and the comfort of upright seating is not lost on me either. Also, I expect that a few generations of development would produce some much improved aircraft, lighter, simpler, more practical, and higher performance. Theres no inherent reason why an airchair has to be heavier than a hang glider (remember that the average hang glider pilot waddles up to launch with about 110 pounds of equipment, only 20 or 30 pounds more than Im flying with now) and the performance can be increased (my airfoil is primitive, and span limits have not been established). Another great potential here is for crash safety, perhaps an opportunity for pilots to walk away from many of the mishaps that would otherwise have added to soaring injury statistics. As a designer and home builder with no interest in anything commercial, I have my own ideas for an ideal airchair, leading mainly in the direction of light weight and simplified control systems. I look forward to seeing more airchair flying, perhaps as a popular third choice for local ultralight soaring, but mainly just to see what develops from this pleasant offshoot of foot launch flying.
Posted on: Tue, 15 Oct 2013 06:39:11 +0000
Trending Topics
© 2015